The present invention relates generally to antennas and, more particularly, to an antenna that scans multiple beams in one direction.
Satellite systems are currently utilized for communication between potentially distant points on the surface of the earth. For example, telephone networks employ such systems to facilitate communication between widely spaced mobile users. In certain such satellite communication systems a satellite is in a non-geosynchronous earth orbit to provide service to a fixed coverage area. These non-geosynchronous satellites often include an antenna having sufficient beamwidth to encompass the entire coverage area. Such non-geosynchronous satellites allow beams to be scanned in one direction that is predominantly a line which may be slightly curved. The beams are scanned to follow the motion of users in fixed positions on the surface of the earth as seen from the nongeosynchronous satellite flying over the users. From the point of view of the satellite, the users are moving so the beams must be scanned to follow the users, or to follow specific areas on the surface of the earth called cells.
Wide beamwidth systems such as that mentioned above generally include certain undesirable features. For instance, the output power of the satellite may be insufficient to adequately illuminate large coverage regions. This situation may be remedied by including more powerful amplifiers on board the satellite for providing increased power to radiating elements of a satellite antenna. However, such enhancements increase the cost of constructing and launching the satellite.
Consequently, alternative antennas such as multiple beam antennas have been developed which address the difficulties associated with conventional wide beamwidth antennas. A multiple beam antenna provides a plurality of narrowly focused beams targeted at individual regions. The output power of a satellite generating these narrow beams is used more efficiently by being directed only to specific regions within a coverage area.
Typically, a multiple beam antenna is capable of electronically scanning the beams along any angular direction to move the beams across two dimensions within the coverage area. To provide the capability of scanning beams across both of the two angular directions, the known multiple beam antennas include a great number of feeds whose inputs are amplitude/phase weighted and then summed by beam combiners to form each beam.
A problem with known multiple beam antennas is that they include many more beam combiners and amplitude phase weighting circuits than required if the beams were required to move along only one angular direction in a straight line or along an angular path that is slightly curved.
Accordingly, it is an object of the present invention to provide an antenna that scans multiple beams along only one angular direction.
It is, accordingly, another object of the present invention to provide an antenna that scans multiple beams along an angular path that is slightly curved.
It is another object of the present invention to provide a multiple beam antenna which scans the beams independently of one another along a common angular direction or angular path.
It is a further object of the present invention to provide a multiple beam antenna which scans the beams along only one angular direction or angular path with each beam being able to be scanned up to at least +/xe2x88x920.7 beamwidths.
It is still another object of the present invention to provide an antenna that forms multiple low sidelobe beams of one or two polarizations and scans them independently of one another along a common angular direction or angular path.
In carrying out the above objects and other objects, the present invention provides an antenna for scanning beams in only one common angular direction. The antenna includes a plurality of feed elements each providing a component beam, and a plurality of fixed beam combiners for combining the component beams into fixed beams. The plurality of fixed beam combiners combine the component beams in a first angular direction to form the fixed beams. A plurality of variable beam combiners combine the fixed beams into scanning beams. The plurality of variable beam combiners combine the fixed beams into the scanning beams. The variable beam combiners are controlled to scan the scanning beams in a second angular direction.
Further, in carrying out the above objects and other objects, the present invention provides a method for scanning beams of an antenna in only one common angular direction. The method includes providing a plurality of component beams. The component beams are then combined into fixed beams. The component beams are combined in a first angular direction to form the fixed beams. The fixed beams are then variably combined into scanning beams to scan the scanning beams in a second angular direction.
The advantages accruing to the present invention are numerous. The antenna scans only in one angular direction allowing it to be simpler and less expensive than an antenna that scans in both angular directions. Low sidelobes are achieved using a fixed distribution among multiple feed elements in the non-scanning direction. Low sidelobes and beam motion in the scanning plane are achieved using a relatively small number of amplitude/phase weights. Further, the antenna provides independent control of each beam within its scanning range.
These and other features, aspects, and embodiments of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings.